Hydrocarbons and other fluids are often contained within subterranean formations at elevated pressures. Wells drilled into these formations allow the elevated pressure within the formation to force the fluids to the surface. However, in low pressure formations, or when the formation pressure has diminished, the formation pressure may be insufficient to force the fluids to the surface. In these cases, a positive displacement pump, such as a piston pump, can be installed to provide the required pressure to produce the fluids.
The function of pumping systems in gas wells is to produce liquid, generally water, that enters the wellbore naturally with the gas. This is typically necessary only on low-flow rate gas wells. In high-flow rate gas wells, the velocity of the gas is usually sufficient that it carries the water to the surface. In low-flow rate wells, the water accumulates in the wellbore and restricts the flow of gas. By pumping out the water, the pump allows the well to flow at a higher gas rate, and this additional produced gas, which eventually is related to additional revenue, pays for the pumping unit.
Operation of the pumping unit can create an area of low pressure beneath the pump compared to high pressure on top of the pump. The differential pressure can become great enough so as to prevent retrieval of the pumping unit by normal means. For example, the differential pressure can result in a pulling force requirement greater than the axial strength of a cable supporting the unit in the well. Pulling up on the cable will thus cause either the cable or a separate shearing mechanism to shear, thus leaving the pumping unit without a connection uphole. For this purpose, the pumping unit can include a fishing neck profile for retrieval using a separate fishing tool. However, without a means for equalizing the differential pressure, retrieval with the fishing tool can also be difficult or impossible.